1. Field of the Invention
The present invention generally relates to telephony performance measurement techniques and, in particular, to an apparatus and method for interfacing with an analog subscriber loop of a telephony communication system and for obtaining, from the subscriber loop, test data that may be used to test the performance of the telephony communication system.
2. Related Art
Initially, telephony networks provided an end-to-end analog communication connection for voice communication. During a telephone call, a user would speak into a telephone, which was coupled to an analog connection, referred to as a “subscriber loop.” The telephone would convert the user's voice into analog signals and transmit the analog signals across the subscriber loop to an analog network, such as the well known publicly switched telephone network (PSTN). The PSTN would then route the analog signals through various analog connections to another subscriber loop coupled to another telephone that receives the analog signals. The receiving telephone then converted the analog signals into sound so that a user at the receiving telephone could hear the conversation of the user at the transmitting telephone.
Each communication connection segment used to transmit the signals from the transmitting telephone to the receiving telephone was analog such that a single end-to-end analog communication connection was effectively provided that communicated the analog signals of the telephone call between the two telephones. Although there was a delay in transmitting from one telephone to the other telephone, each analog signal experienced approximately the same delay. Therefore, as long as the delay was small (e.g., on the order of about one second or less), users did not usually notice the delay.
Although most end-to-end analog communications were fairly reliable, problems sometimes developed that would cause excessive noise, cross-talk, or other similar performance degrading effects. To test the quality of the signals communicated by the analog network, an operator would usually place a call and listen to the sound produced by the analog signals transmitted through the network. If the operator detected significant performance degradation, such as significant noise, cross-talk, etc., the communication segments and devices used to transmit the signals would be further tested in an attempt to isolate and correct the problems causing the performance degradation.
Recently, many telephony networks have been redesigned to communicate digitally to improve the performance of the networks. However, due primarily to the expense of installing digital subscriber loops, many of the subscriber loops used to transmit voice signals have remained analog. Therefore, during a telephone call, a user typically speaks into a telephone that converts the user's voice into analog signals. These analog signals are then transmitted across an analog subscriber loop to a digital telephony network. At some point in the digital network, the analog signals are converted into digital signals and transmitted across digital connections. Prior to being communicated across the subscriber loop coupled to the receiving telephone, the digital signals are converted back into analog signals so that the signals are compatible with the subscriber loop. Therefore, the operation of the foregoing digital telephony network is similar to prior analog telephony networks, except that the signals communicated by the foregoing digital telephony network are converted into digital signals for transmission across at least a portion of the network.
Unfortunately, the conversion of the analog signals into digital signals can cause certain problems. For example, the digital portion of some networks utilizes packet switching techniques, in which the digital signals are transmitted as separate packets through the digital portion of the network. Although the packets are transmitted from the same beginning point and the same ending point within the digital portion of the network, the path for each packet may be different. Therefore, the delay experienced by each packet may be significantly different than the delay experienced by other packets. When the packets are received at the ending point, the packets are reassembled into the correct order before being converted back into analog signals so that the analog signals accurately represent the conversation being communicated. The aforementioned packet switching techniques introduce a delay, which is sometimes noticeable by the users associated with the telephone call.
Due to the various problems that can be caused by utilizing a digital network in communicating voice signals, such as the delay introduced by packet switching, it is desirable to test the transmission quality of digital telephony networks more frequently as compared to traditional analog telephony networks. Therefore, various devices that enable automatic testing of voice signals in a digital telephony network have been developed. However, most of these devices are designed to interface with the digital portion of the telephony network and are designed to test the digital signals being communicated by the digital portion of the telephony network. The inventor of the present invention believes that a superior voice quality testing device can be implemented, if the testing device is interfaced at an analog end of the network and is configured to test the analog signals communicated at this analog end during a telephone call.
Thus, a heretofore unaddressed need exists in the industry for providing an improved apparatus and method for enabling automatic testing of voice signals at an analog end of a digital telephony network.